1. Field of the Invention
Embodiments of the present invention relate in general to the field of semiconductor device fabrication. More particularly, embodiments of the invention relate to an apparatus for dispensing a photo-resist in a uniformly coat on a semiconductor wafer.
This application claims priority to Korean Patent Application No. 10-2005-0115742 filed on Nov. 30, 2005, the entire contents of which are hereby incorporated by reference.
2. Description of the Related Art
Semiconductor devices are fabricated through the application of a complex sequence of individual processes. Very specialized fabrication equipment has been developed to perform these processes. Precision application of fabrication processes by this specialized equipment is critical to the ultimate quality of the semiconductor devices being fabricated. Many individual fabrication processes are repeatedly applied to a semiconductor wafer during the sequence of processes.
Exemplary fabrication processes include processes adapted to form material layers on the semiconductor wafer, processes adapted to coat the semiconductor wafer with a photo-resist, photolithography processes adapted to transcribe a circuit pattern onto a photo-resist layer, etching processes adapted to selectively remove a portion of a material layer, implantation processes adapted to selectively implant impurities, etc.
Photolithography processes are important components within the sequence fabrication processes used to manufacture semiconductor devices. Such processes are critical to the determination of certain critical dimensions and geometries that implement the circuitry of the semiconductor devices. These critical dimensions are constantly reduced in attempts to maximize the productivity of semiconductor devices per unit wafer. This downward pressure on critical dimensions places constant performance demands upon the precision of conventional photolithography processes.
The equipment used to perform photolithography processes includes photo spinner equipment and/or exposure equipment. Photo spinner equipment comes in a variety of forms from different suppliers, but it generally includes a spin coater unit adapted to coat a photo-resist solution onto a wafer, a plurality of baking units adapted to bake and hardening the spin coated photo-resist, an exposure unit adapted to selectively expose the photo-resist formed on an edge portion of the wafer and thereafter selectively expose the photo-resist using a mask film such as a reticle, a developer unit adapted to develop the photo-resist, and a wafer transfer and interface unit adapted to transfer the wafer between the other units.
The spin coater typically rotates the wafer at a predetermined speed (e.g., 400 rpm) and applies a fixed volume of photo-resist to the center of the rotating wafer in order to uniformly spread the photo-resist over the surface of the wafer. Where an insufficient volume of photo-resist is dispensed onto the center of the wafer the resulting photo-resist layer will be too thin or have gaps formed therein. On the contrary, where an excessive volume of photo-resist is used the overall fabrication costs will rise as a large volume of photo-resist is wasted. Thus, the development of photo-resist dispensing apparatus associated with spin coaters has been the subject of intense research and development.
There are significant obstacles to the precision operation of a photo-resist dispensing apparatus. For example, if the photo-resist being dispensed contains gas bubbles poor quality photo-resist layers will result. An unstable or interrupted supply of photo-resist solution to the dispensing apparatus will also result in poor quality photo-resist layers.
A conventional photo-resist dispensing apparatus adapted to remove gas bubbles in a photo-resist solution is disclosed, for example, in U.S. Pat. No. 6,402,821, the subject matter of which is hereby incorporated by reference. FIG. 1 is a schematic diagram illustrating a conventional photo-resist dispensing apparatus.
As shown in FIG. 1, the conventional photo-resist dispensing apparatus includes a tank 41 having an internal space adapted to hold a photo-resist solution, an opening/closing valve 70 configured to control a supply of the photo-resist solution from tank 41, an intermediate tank 7 configured to remove gas from the photo-resist solution by temporarily storing it, a filter 5 configured to remove any contaminate particles from the photo-resist solution supplied from intermediate tank 7, a discharge valve 42 configured to control a discharge volume of the photo-resist solution, and a dispensing nozzle 3 configured to dispense the photo-resist solution in a controlled manner onto the upper surface of a wafer W as it rotates on a platen 2.
Tank 41 will provide the photo-resist solution through opening/closing valve 70 and a supply line 43 under the force of gas pressure (e.g., nitrogen gas) introduced into tank 41. The introduction of pressurized gas forms gas bubbles in the photo-resist solution within tank 41. Thus, intermediate tank 7 is required to remove the bubbles before being dispensed.
FIG. 2 is a cross-sectional view of intermediate tank 7 shown in FIG. 1. As is shown in FIG. 2, intermediate tank 7 includes; a body 71 having a defined internal space passing photo-resist solution via supply line 43, and an exhaust line 72 coupled to an upper part of body 71 and adapted to discharge gas bubbles precipitating out of the photo-resist solution, and a bubble filter 73 installed in an inlet or an inner portion of exhaust line 72 and adapted to filter discharged gas bubbles. Bubble filter 73 typically includes a membrane configured to prevent the photo-resist solution from passing through exhaust line 72, and selectively pass only gas from body 71.
In the illustrated example, exhaust line 72 is coupled to one side of the upper portion of body 71 while supply line 43 is coupled through the other side of body 71 to be substantially in parallel with exhaust line 72.
Unfortunately, the conventional photo-resist dispensing apparatus suffers from a number of problems. First, it has a disadvantage in that the photo-resist solution delivered within body 71 may pass from the inlet of supply line 43 to the output of supply line 43 without flowing through the bubble filter 73 configured in exhaust line 72. Thus, bubble filter 73 works most effectively on gas bubbles proximate the opening of exhaust line 72. This result yields unreliable results in the removal of bubbles.
In a related vein, the conventional photo-resist dispensing apparatus has the disadvantage of discharging bubbles not only through exhaust line 72, but also through the outlet of supply line 43 coupled to filter 5. Where the photo-resist solution contains a great volume of gas bubbles, many gas bubbles may pass directly through intermediate tank 7 without being removed from bubble filter 73. Any gas bubbles in the photo-resist solution will adversely effect the quality of wafer coating, and thus decreases a productive yield in the semiconductor devices being fabricated.